Hi, I found: http://hybridauth.sourceforge.net/index.html
Which is a well documented class for login/integration with up to 29 diffrent providers.
EDIT
Figured stuff out so go here if you are curios
http://www.yiiframework.com/forum/index.php/forum/13-extensions/
It’s easy enough. 
And even easier to just grab a couple similar extensions - search for Facebook, Twitter, etc in the extensions section of the Yii site.
Or the wiki.
If you still don’t know where to start, and/or how to attack this, I’ll probably throw in some code for you - if I’m not beaten by others.
Edit:
http://www.yiiframework.com/doc/guide/1.1/en/topics.auth#login-and-logout
Implement UserIdentity::authenticate - make it use that multiauth extension (instead of a database/plain text).
That’s probably all you need to do, if using the standard generated Yii app.
By the way: nice find! 
I am about to write an app where I need it, so perfect timing.
It’s fairly new too. Not bad.
EMBRACE YOURSELFS! WALL OF TEXT IS COMING
This got a bit long but I think its an interesting find. Mostly Because hybridAuth has already taken care of all the headaches it is to integrate a shitload of diffrent api’s etc.
They even have working full blown social hub examples. The only thing left for us is to make it work in yii also.
I looked at all the extensions,tried them, the only one that was updated/worked well was yii-facebook-opengraph It is nothing wrong with it, I shared a demo-app where I used that and browserid/persona login.
So I already have all the functions for creating a new User and connecting it to a provider.
I’m currently building an app where I will need more then those two though. Looked at twitters/google’s own pages and many blog posts, Sending tweets was easy enough But never quite got hang of the auth part:p
So when I by pure chance stumbled over this due to an 2 year old post here on the forum I got super excited XD The docs and examples are great, But with all those files/classes changing one thing screws up another and after I while I stranded on some I didn’t know how to fix
Even though I realise it really shouldn’t be that hard:p
But I really need it and I think it would be appreciated here.
Perhaps going thrue the extensions for cakePHP and/or codeigniter would be usefull.
I believe a module would be the most convenient way to attack this, It’s how I got the furthest in my attempts XD
I think it should work something like this:
*The user presses a link for one provider,which creates an request to the module which does some magic, and when done runs a method in whatever User model the developer has and passes the needed info to create a new user and connect it to the provider_uid.
*I think having some yii methods for example sending a tweet or display available userinfo.
could be usefull.
Never had much success trying to make a module of it:(
Putting it in the root and doing ajaxRequests seems to work a bit better. Not really cool though.
Ran across this library on HackerNews recently…already has a configuration for yii, so might be a good way to get this moving. HybridAuth is definitely more complete, but this has yii "support"… http://opauth.org/